3D Printing with Liquid Crystal Elastomers: New Insights into Targeted Material Control

Liquid crystal elastomers (LCEs) belong to a class of soft synthetic materials that can deform under temperature changes. They mimic the behavior of muscles, contracting and relaxing in response to external stimuli. The 3D printing of these materials opens up new application possibilities in robotics, prosthetics, and adaptive textiles.

Precisely controlling the properties of these materials requires extruding elastomer-forming ink through a 3D printer nozzle. This process alters the internal structure of the material, aligning rigid molecular components known as mesogens. Until now, optimizing this process has required extensive trial and error.

A research team from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), Princeton University, Lawrence Livermore National Laboratory, and Brookhaven National Laboratory has developed a systematic approach for printing LCEs with controlled molecular alignment. By using X-ray characterization during printing, the researchers were able to precisely determine how mesogens arrange within the printed material.

“When this project began, we simply didn’t have a good understanding of how to precisely control liquid crystal alignment during extrusion-based 3D printing,” said first author Rodrigo Telles, a SEAS graduate student, Academic Cooperation Program scholar and collaborator with Lawrence Livermore National Laboratory. “Yet it is their degree of alignment that gives rise to varying amounts of actuation and contraction when heated.”

By adjusting nozzle geometry, extrusion speed, and temperature, the desired molecular alignment can be achieved. The researchers found that hyperbolically shaped nozzles produced more uniform and better-aligned structures than conventional print heads. The resulting materials exhibit controlled mechanical properties, making them suitable for applications such as artificial muscles or adaptive structures.

“In the 3D printing community, most of us use a relatively small number of commercially available printheads. This study showed us that it’s important to pay attention to the details of both nozzle geometry and flow – and that we can exploit them to control material properties,” Davidson said.

“The ability to ‘see’ into liquid crystal elastomers and quantify their alignment at the microscale during printing via wide angle X-ray scattering measurements has provided a fundamental framework of their processing-structure-property relationships for the first time,” Lewis said.

This research provides a foundational methodology for controlling the structure-property relationships in LCEs. The study was supported by the National Science Foundation and the U.S. Army Research Office. Additional funding came from Lawrence Livermore National Laboratory projects focused on shape-changing elastomer structures, as well as resources from Brookhaven National Laboratory.